1. Field of the Invention
The present invention relates generally to suspension systems for vehicles, and more particularly is directed to an improvement in a suspension system used for supporting each of steerable wheels in a vehicle.
2. Description of the Prior Art
A suspension system for supporting each of steerable front wheels of a vehicle is provided with a knuckle structure which is supported to be able to move up and down and to swing with an axis of oscillation extending up and down in relation to a body of the vehicle by suspension arms connected to the body and has a wheel spindle for supporting the steerable front wheel. The knuckle structure is further provided with a knuckle arm extending therefrom to be connected with a tie rod which is moved to steer the steerable front wheel supported by the knuckle structure.
In general, for bringing stabilized controllability and comfortableness in driving on a vehicle, a suspension system for supporting each of wheels of the vehicle is required to permit the wheel supported thereby to move backward and forward easily when a force working in the vehicle longitudinal direction is applied to the wheel and to prevent the wheel from moving freely when a force working in the vehicle transverse direction is applied to the wheel.
In view of such requirements to suspension systems as mentioned above, there has been previously proposed a suspension system for a vehicle which is operative to support a steerable front wheel of the vehicle in such a manner that the steerable front wheel is easy to move in the vehicle longitudinal direction and hard to move in the vehicle transverse direction, as disclosed, for example, in U.S. Pat. Nos. 4,155,566 or 2,882,065. In the suspension system thus proposed previously, a knuckle structure is divided into upper and lower knuckle members and the upper knuckle member is connected through an elastic member with the lower knuckle member so that the whole knuckle structure becomes relatively flexible in the vehicle longitudinal direction and relatively hard in the vehicle transverse direction.
In more detail, in the suspension system disclosed in U.S. Pat. No. 4,155,566, a lower knuckle member which is connected through a lower suspension arm with a body of the vehicle is provided with a wheel spindle on which the steerable front wheel is mounted, a knuckle arm connected to a tie rod and a joint pin which extends toward the inside of the body in the vehicle transverse direction. The joint pin extending from the lower knuckle member is coupled rotatably with the lower portion of an upper knuckle member which is connected through an upper suspension arm with the body. The lower knuckle member is further provided with a supporting sleeve member which is incorporated with the lower knuckle member to surround the lower portion of the upper knuckle member with an elastic sleeve member disposed between the inner surface of the supporting sleeve member and the outer surface of the lower portion of the upper knuckle member.
With such an arrangement, the lower knuckle member is able to be easily swung with the joint pin as the center of oscillation within an angular area limited based on elastic deformations of the elastic sleeve member and hard to move the direction along which the joint pin extends, so that the steerable front wheel supported by the lower knuckle member is easy to be move backward and forward by a force applied thereto in the vehicle longitudinal direction and hard to be moved laterally by a force applied thereto in the vehicle transverse direction.
In the suspension system disclosed in U.S. Pat. No. 2,882,065, a lower knuckle member is also provided with a wheel spindle, a knuckle arm and a joint pin which extends toward the inside of a body of the vehicle in the vehicle transverse direction to be coupled rotatably with the lower portion of an upper knuckle member. The lower knuckle member is further provided with front and rear supporting portions facing each other in the vehicle longitudinal direction with the upper knuckle member between, and a pair of elastic spacers are disposed respectively between the front supporting portion and the upper knuckle member and between the upper knuckle member and the rear supporting portion.
With such an arrangement, the lower knuckle member having the wheel spindle on which the steerable front wheel is mounted is permitted to move easily in the vehicle longitudinal direction and prevented from moving freely in the vehicle transverse direction.
However, in the event of the suspension systems proposed previously as described above, the knuckle structure is complicated in construction and thereby the production cost of the system is increased. The joint pin used for connecting the lower knuckle member with the upper knuckle member is required to be constituted with high precision because the movement of the knuckle structure in the vehicle longitudinal direction is caused by the lower knuckle member moving to swing with the joint pin as the center of oscillation in relation to the upper knuckle member. This results in a problem of difficulties in manufacture in case of practical use of the previously proposed suspension systems. Further, each of the upper and lower knuckle members is anticipated to be prevented by the joint pin connected with the lower portion of the upper knuckle member from inclining toward the inside or outside of the body of the vehicle, that is, the joint pin and the lower portion of the upper knuckle member coupled with the joint pin are expected to maintain the steerable front wheel to be appropriate in its camber when the steerable front wheel is almost zero in steering angle. However, the joint pin and the lower portion of the upper knuckle member must be engaged with each other so as to have a certain clearance therebetween in order to permit the joint pin to rotate, and therefore the steerable front wheel is apt to be varied in its camber under a condition in which the steerable front wheel is almost zero in steering angle.